1. Field of the Invention
This invention is generally concerned with devices for scraping the insides of pipes in general and oil and/or gas well casings in particular.
2. Description of the Prior Art
Pipes of all kind are subject to becoming clogged with the materials they convey. For example, in the drilling, completion or workover of an oil well, the interior of the well casing or other conduit is exposed to a variety of foreign materials which often tend to adhere to the internal surface of the conduit. Drilling mud, paraffin, cements, rust and/or scale build up in ever increasing layers until finally the flow of fluids through the pipe is effectively choked off. Therefore, to permit the unimpeded passage of pumping equipment, perforating equipment and the like into and out of well casings, it is obviously desirable that all foreign substances adhering to the interior walls of the casing first be removed. Additionally, burrs resulting from perforation operations sometimes prohibit the free passage of packing and other elements through the well, and such burrs of necessity must therefore be removed.
To effect such removal, a number of scraping tools have heretofore been employed. Most commonly used prior art scrapers have been characterized by the fact that they employ rotating pipes to effect scraping operations. Most of these in turn are also characterized by the fact that they have only a limited effective diametrical range of operation. For example, it is known that a seven inch interior diameter well casing may have five or more different internal diameters, dependent on the casing weight required for the particular installation. The thickness and hardness of the materials deposited on the interior of the pipe are also subject to a great deal of variation over relatively short distances within the pipe. As a result, the scraping apparatus hereto available required the installation of various sizes of blade blocks, one at a time, on the tool support in order to scrape the full range of internal diameters provided in seven inch casing. Moreover, a great deal of time and effort is needed to assemble a string of pipes to carry out any scraping operation based upon a powered rotation of the pipes to which such scrapers are attached.
It has been long recognized that scraping devices capable of being operated from a cable lowered into such a pipe would save a great deal of time. However, most prior art cable operated scrapers have not proven to be particularly effective. Many operators regard cable operated scrapers as being especially ineffective in scraping in an "upward" direction, that is, from the bottom of the well toward the top. Moreover, such devices also have not proved to be particularly useful for scraping heavily caked walls. Furthermore, they also heretofore have not been able to scrape the entire 360 degrees of the inner circumference of such pipes. Cable operated devices They also have been more prone to becoming lodged in clogged pipes than are their rotary operated counterparts. Furthermore, most prior art cable operated pipe scraping devices are not susceptible to automatic adjustments of the effective working diameter of the scraping elements during operations. Hence, these devices have to be practically disassembled in order to achieve any scraping diameter adjustments. In many instance, this implies more passes of the scraper through a clogged pipe. It should also be noted that most cable operated scrapers are not particularly suited to ready conversion for use in rotary powered scraping operations.
Moreover, most automatic, diameter adjusting scraper devices are based upon a spring biased scraping mechanisms which do not readily withstand the loads and rough handling inherent in scraping operations. Such springs are frequently the first part of the device to fail. Moreover, many prior art scraping devices do not incorporate a simple means for compensating for wear on their scraper blades; thus they require replacement of the entire blade assembly whenever any significant wear takes place. Additionally, the mounting of blade blocks on most prior art apparatus is such that if a jam occurred between the scraper surface and an obstruction in the casing, it was generally quite difficult to pull the tool free since the spring loaded cutting surfaces are usually permanently biased in the outward direction once the scraper is inserted into the pipe. It is therefore apparent that there is a distinct need for an improved, more flexible, readily adjustable scraping apparatus for pipes of all kinds and oil and gas well casings in particular. This need is particularly apparent in the case of pipe scrapers operated by pulling upon cables attached to devices of this type.